Production of aviation gasoline



NOV' 20, 1945- J. A. ANDERSON, JR

PRODUCTION QF AVIATION GASOLINE Filed July 2l, 1944 glow nl 4 hllrtzow(7W Im/NTOR.

Patented Nov. 20, 1945 UNITED STATES PATENT OFFICE PRODUCTION OFAVIATION GASOLINE James A. Anderson, Jr., Goose Creek, Tex., as-

sig'nor to Standard Oil Development Company. a corporation of DelawareApplication July 21, 1944, Serial No. 545,976

4 Claims. (Cl. 196-52) The present invention relates to a process forproducing aviation fuel from catalytically cracked naphtha. Moreparticularly it is concerned with a process for recovering iso-parafiinsfrom catalytically cracked naphtha substantially free from aromatcs andolens. In its more specific aspects the present invention contemplatesthe solvent extraction of a selected catalytically cracked naphthafraction and the recovery of a fraction from the solvent raiinatecomprising substantially the iso-parafns.

During the last few years catalytic cracking has reached the stage ofdevelopment where it has become an important tool of the petroleumreiiner in producing aviation gasoline. While the catalytically crackednaphtha is suitable for the production of aviation gasoline, its use isopen to some objection in that drastic chemical treatment is necessarybefore the fuel is suitable for use in the aviation motor. For example,it is often necessary to treat the catalytically cracked naphtha with alarge amount of sulfuric acid to destroy the olefins or to hydrogenatethe whole I fraction to make it suitable for aviation fuel. When acidtreatment is contemplated, it is often necessary to supplement the acidtreatment with inhibition to provide stability for the fraction.

In accordance with the present invention it is unnecessary to resort tothe aforementioned processes in producing aviation fuel components fromcatalytlcally cracked naphtha. In my invention, I extract a fractionboiling up to about 250 F. with a solvent which will separate paraiinicconstituents from the alicyclic, olenic and aromatic constituents toobtain a fraction comprising essentially the iso-parafns. In the solventextraction the alicyclic, oleflnic'and aromatic hydrocarbons are largelyconcentrated in the extract and may then be recovered therefrom by atreating operation which may involve a second extraction with a solvent,distillation and hydrogenation, as may be desired. My invention allowsthe obtaining, from a catalytically cracked fraction, of desirableaviation fuel components without treatment of the total fraction.

little aromatics,`it is possible to recover the isoparalns by a veryinexpensive process as compared to the more expensive processes aslpracticed in the art.

The present invention will be better understood by reference to theaccompanying single gure which is a iiow plan illustrating a preferredembodiment.

Referring now to the drawing, numeral I I designates a feed line throughwhich a gas oil boiling in the range of about 450 to 800 F. isintroduced into catalytic cracking zone I2. Catalytic cracking zone I2may be any type of catalytic cracking operation but for purposes ofillustration, it will be assumed that it embodies a cracking operationof the so-called fluid catalyst type. In catalytic cracking zone I2, thegas oil is subjected to cracking conditions employing temperaturesbetween 800 and 1100" F. and pressires up to about 50 pounds per squareinch. Preferably, pressures of the order gf 15 pounds per square inchare employed. A silica-alumina catalyst either of natural or syntheticorigin may be employed satisfactorily.

'I'he catalytic cracking zone I2 may be operated on either a naphthenictype of gas oil or a paralnic type of gas oil. It has been observed thatwhen employing either naphthenic or parafnic gas oils at low conversionand high throughputs formation of iso-paralns is favored; irrespective,however, of the operation of the catalytic cracking zone I2, it ispossible to practice my invention and obtain a satisfactorily pure iso-In the catalytic cracking of a gas oil for ex' is possible to solventextract such a fraction and obtain a railinate fraction comprisingessentially the iso-paralilns. By virtue of my discovery that thisfraction contains substantially no n-paralns paraiin fraction. Theconditions obtaining in catalytic cracking zone I2 are known in the artand do not form part of this invention but are given in some detail toallow proper understandtion zone I4. It is, of course, well understoodthat the distillation zone I4 may comprise a number of distillationtowers each provided with heating means I5, but for ease of descriptionin the present invention, reference will be made to a single tower.Distillation zone I4 is provided with a line I6 for discharge of heavierconstituents, line I'I for removal of components boiling above 250 F.,line I8 for recovery of a fraction bollingbetween about 105 and 250 F.,and line I9 for dis-` charge of products boiling below about 105 F.which may be further processed for recovery of valuable vaporousconstituents. The desired and by virtue of the fact that it containsvery cracking fraction. boiling at temperatures in the 2E range betweenabout 105 and 250 F. is discharged from fractionatlng zone I4 by line I8and is introduced into an extraction zone 22. Extraction zone 22 may beeither an extractive distillation zone, employing countercurrent contactbetween a vaporous hydrocarbon feed and a liquid selective solvent, or aconventional liquid phase solvent extraction zone, employingcountercurrent contact between a liquid hydrocarbon feed and a liquidselective solvent. It will be understood, of course. by those skilled inthe solvent extraction art that. when extractlve distillation isemployed'in zone 22, it may be desirable to process a fraction having anarrower boiling range than is described above. For purposes ofillustration, however, it will be assumed that extraction zone 22 is ofthe conventional liquid-liquid phase type, the extraction is carried outon a fraction having the boiling range speciiled above, and the solventis introduced into zone 22 through lines 20 and 2|.

The type of solvent employed in extraction zone 22 is selected from theclass of compounds illustrated by phenol, furfural, diethylene glycol,triethylene glycol and the polyethylene glycols and mixtures thereof.For purposes of illustration only it may be assumed that a mixture ofpolyethylene glycols and ethylene glycol is employed in extraction zone22 as the selective solvent. For best results in the process to obtain arafiinate comprising essentially iso-paraillns a solvent to hydrocarbonratio in the range between :1 and 15:1 is desirable. The temperatureobtaining in solvent extraction zone 22 may be varied considerably, buta temperature of the order of about 150 F. at atmospheric pressure isusually desirable. To obtain the iso-paraftln substantially free fromthe alicyclic, olefinic and aromatic hydrocarbons, solvent extractionzone 22 should include 30 to 50 stages in which the conditions areadJusted to obtain ramnate and extract phases which are withdrawntherefrom by lines 23 and 24, respectively. 'I'he raiilnate phase,containing a small amount of solvent is discharged by way of line 23into the solvent stripper 25 which is provided with a heating means 26.The solvent is taken oi! from solvent stripper 25 by line 2| and theiso-paraiiins are discharged from stripper 25 by line `21 and are thensuitable for use as an aviation fuel constituent or may be employed as afeed stock for an alkylation process as desired. It is to be understoodby the skilled worker that, depending on the boiling point of thesolvent employed, in some instances instead of the iso-parain beingtaken overhead and the solvent withdrawn as bottoms from tower 25 in themanner illustrated, the solvent may be distilled overhead and theiso-paraffins withdrawn as bottoms by way of line 2|.

The extract phase is introduced by line 24 into a second solventstripper 28 which is similar to stripper 25, and is equipped with aheating means 29. Solvent is recovered from stripper 28 by line 20 andreturned to extraction zone 22 while the hydrocarbon constituents of theextract are discharged through line 30 and are introduced thereby into asecond extraction zone 3|. In some instances it may bev desirable todischarge the extract hydrocarbons from the system without processingthem through extraction zone 3|. In this particular instance, valve 32in branch line. 33 would be opened and valve 34 in line 30 would beclosed oil.

For purposes of illustration, however, it is assumed that it is desiredto process the extracted hydrocarbons through the extraction zone 3|. Asolvent similar to that employed in extraction zone 22 is introducedthrough line 35 and conditions are adjusted to obtain railinate andextract phases. In extraction zone 3|, it will be desirable to employ asolvent to hydrocarbon ratio in the range between about 4:1 and 12:1,temperatures of the order of about 150 F., with atmospheric pressures,and utilizing between about 15 to 25 stages. The solvent may be selectedfrom the type of solvents employed in extraction zone 22 with theunderstanding that adjustments may be made for the composition of thehydrocarbons in the extract discharged to zone 3|.

The rallinate phase is withdrawn from extraction mne 3| through line 36and introduced thereby into a third solvent stripper 31 in whichtemperature and pressure conditions are adjusted by heating means 38.Solvent is withdrawn'from stripper 31 by line 39 for reuse in theprocess while a hydrocarbon component comprising essentially oleiinicand alicyclic constituents is discharged from stripper 31 by line 40.These hydrocarbons may be discharged from the system by opening valve 4|but preferably are routed to hydrogenation zone 42 through line 43controlled by valve 44. It is understood, of course, that valve 4| isclosed oi when the alicyclic and oleflnic constituents are routed tozone 42.

The conditions prevailing in hydrogenation zone 42 have been wellestablished in the patent art and are adjusted to obtain a substantiallysaturated material which may be discharged from zone 42 through line 45,hydrogen for the saturation of the hydrocarbons in zone 42 beingintroduced through line 46. The effluent discharged from zone 42 by line45 may be employed as an aviation fuel as is, or it may be blended withthe isoparains recovered by line 21 or blended with other well knownblending agents such as isopentane and tetraethyl lead.

The extract phase discharged from extraction zone 3| by line 41 isintroduced thereby into a fourth solvent stripper 48 equipped withheating means 49 and provided with lines 50 and 5|. Solvent is withdrawnfrom stripper 48 through line 50 while aromatics are recovered by way ofline 5I. It will be understood, of course, that the amount of aromaticsrecovered will necessarily be small by virtue of the boiling range ofthe fraction recovered by line |8. The only aromatics that will beincluded with the stream from line 5| will be benzene or toluene whichare also valuable constituents of aviation fuel and may be used as such,as solvents, or as may be desired.

The blending of the streams or portions of thc streams from lines 21, 45and 5| to produce an aviation fuel may be accomplished by line 52,branch line 53 containing valve 54, branch line 55 containing valve 56,and branch line 51 containing valve 58. When it is desired to blendisoparailins from line 21, saturated hydrocarbons from line 45 andaromatics from line 5|, valves 58, 56 and 54 may be opened to allow theisoparaiiins, saturated hydrocarbons and aromatics to flow into line 52,where they admix to produce a finished aviation grade fuel.

In a typical operation in accordance with the present invention, 'afraction having a boiling range between and 210 F. may be obtained fromthe fractionatng zone |4 of a fluid catalyst cracking operation. llhisfraction comprises hydrocarbons in accordance with the followingcomposition:

Table! Per cent Saturates 50.0 Olefins 47.0 Aromatics 3.0

Table 1r A fraction of the above composition is blended with 4 cc. oftetraethyl lead per gallon and tested for octane number and it is foundthat the octane'l number of the leaded fraction is 94.7 Since theequivalent octane number of the aromatics is known to be about 95 andsince thatiof the corresponding olefins is known to be'considerablylower, the high octane number of the rainate fraction demonstrates thatit is largei., isoparafiinic in nature. By milding treating the ramnatehaving the composition shown. in Table II with sulfuric acid; it ispossible to obtain-a fraction comprising essentially the isoparains. "f

The extract resulting from the above described operation is freed ofsolvent and consists largely of oleiinic components and alicyclichydrocarbons. These materials on hydrogenation produce excellentaviation fuel components.

From the above typical operations in accordance with my invention, itwill be obvious to the skilled worker that a substantial contribution tothe art of producing aviation fuels has been made. Not only has it beenshown that it is unnecessary to treat the catalytically cracked naphthaof a suitable boiling range drastically and thereby destroy valuableconstituents but it has also been shown that it is possible to recoversubstantially all components of the catalytically cracked naphtha and tomake them available for use in aviation fuel. I

The invention is susceptible to considerable variation in the operationof the several steps making up my process. For example the c'onditionsobtaining in extraction zones 22 and 3i may be varied widely dependingon the type of solvent being employed therein and the boiling range ofthe fractions being extracted.

In a similar manner the treatment of the isoparaflin concentraterecovered by line 21 may also be varied. When Ithe isoparafflnconcentrate forms a feed to an alkylation system it will be unnecessaryto remove the residual olens contained therein. On the other hand, whenthe isoparailin is employed as a blending agent, it may be desirable totreat out the residual olens by subjecting the fraction to the action ofa treating agent such as sulfuric acid or any other olefin reactingmaterials.

Percent Saturates 91.7 Oleiins 6.9 Aromatics 1.4

The present invention is not applicable to all types of crakingoperations. For example, the conventional thermal cracking operationproduces products which are unsuitable as charge stocks for my process.It is reiterated that it is only the catalytic cracking operation whichproduces a suitable feed to be processed as described. And it is onlythe selected fractions of the catalytically cracked products that can betreated in accordance with my invention to recover the isoparaillns.Speciiically, my invention is based on the discovery that the fractionscontained in catalytically cracked naphtha boiling below about 250 F.comprises essentially isoparins, oleiins, alicyclics with very littlenormal paramns and aromatics. This discoverey is of considerableimportance since it is possible to recover substantially all theisoparamns from the hydrocarbons with which they are usuallyassociated.-

If a fraction having a corresponding boiling range from a vthermalcracking operation is treated in accordance with the steps of theprocess, a much inferior product containing normal parafdns as well asisoparalns is obtained.

One greatadvantage of operating in accordance with the present inventionis the chemical stability of the product obtained therefrom. Forexample, in the conventional treating processes to produce aviation fuelfrom catalytically cracked naphtha, the products frequently deterioratein storage unless the treatment -given the products is suillcientlysevere to destroy valuable constituents contained therein and unless thetreatment is supplemented by use of oxidation inhibiting agents. In myprocess all of these disadvantages are overcome. The isoparailinconcentrate, comprising predominately the saturated hydrocarbons isquite stable in storage. The small amount of oleiin components may beremoved by a mild chemical treatment. 0n the other hand the hydrocarbonsconcentrated in the extract phase may be subjected to hydrogenationtreatment which forms a stable product. In the prior processes in whichhydrogenation was employed to form a stable product by hydrogenation ofthe total fraction some 50% of the fraction was'submitted unnecessarilyto the hydrogenation treatment.

The nature and objects of the present invention having been describedand illustrated, what I wish to claim as new and useful and secure byLetters Patent is:

1. A method for producing an olefin-free aviation grade fuel comprisingthe steps of subjecting a catalytically cracked naphtha to distillationto separate a fraction boiling between 105 and 250 F., solventextracting said fraction to form a first railinate fraction and a firstextract fraction, separating said first rainate fraction from said firstextract fraction, subjecting said rst extract fraction to a secondextraction step to separate a second raffinate fraction and a secondextract fraction, subjecting said second ramnate fraction to a step ofcatalytic hydrogenation capable of converting oleflns therein tosaturated hydrocarbons, "removing product froml the hydrogenation stepand blending it with at least portions of the rst railinate fraction andthe second extract fraction to produce an aviation grade fuel.

2. A method for obtaining an aviation grade motor fuel comprising thesteps of subjecting a A petroleum fraction boiling in the range of 450to 800 F. to catalytic cracking in a cracking zone containing a catalystand maintained at a temperature between 800 and 1100 F., removingcracked product from the catalytic cracking zone, distilling saidcracked product to separate a fraction boiling in the range of 105 to250 F., subjecting said fraction to a first solvent extraction step toform a rst ramnate comprising a major portion of isoparailins and a rstextract, separately removing the first ramnate and first extract fromthe first extraction zone, passing the first extract to a secondextraction zone and separating it into a second rainate comprising amajor portion of unsaturated hydrocarbons and a second extractcomprising a major portion ot aromatic hydrocarbons, separately removingthe second extract and second raillnate from the second extraction zone,subjecting the hydrocarbons in the second rafnate to hydrogenationconditions capable of saturating substantially all of the unsaturatedhydrocarbon therein, and blending at least a portion of the hydrocarboncomponents from the first raflinate, the second hydrogenated raiiinateand the second extract to produce a blended aviation grade fuel.

3. A method for producing an olefin-free aviation grade fuel comprisingthe steps of fractionally distilling a catalytically cracked naphtha toseparate a fraction boiling between 105 and 250 F., solvent extractingsaid fraction to form a first raiilnate fraction and a first extractfraction, separating said rst rainate fraction from said iirst extractfraction, subjecting the ilrst extract fraction to a second extractionstep to separate a second rainate fraction and a second extractfraction, subjecting said second railinate iraction to a step ofcatalytic hydrogenation capable of converting oleilns therein tosaturated hydrocarbons, .removing product from the hydrogenation stepand blending it with at least a portion of the ilrst raillnate fractionto produce an aviation grade fuel.

4. A method for obtaining an aviation grade motor fuel comprising thesteps of subjecting a petroleum fraction boiling in the range oi 450 to800 F. to catalytic cracking in a cracking zone containing a-catalystand maintained at a temperature in the range of 800 to 1100 F., removjing cracked product from the catalytic cracking zone, iractionallydistilling the cracked product to separate a fraction boiling in therange of to 250 F" subjecting said fraction to a rst solvent extractionstep in a rst extraction zone to form a rst raillnate comprising a maiorportion of isoparafiins and a rst extract, separately removing the rstraffinate and iirst extract trom the rst extraction zone, passing thefirst extract to a second extraction zone and there separating it into asecond railinate comprising a maior portion of unsaturated hydrocarbonsyand a second extract comprising a .major portion oi aromatichydrocarbons, removing the second raillnate from the second extractionzone, subjecting the second raffinate to hydrogenation conditionscapable of saturating substantially all of the unsaturated hydrocarbonstherein and blending at least a portion of the hydrocarbon componentsfrom the rst rafiinate and the second hydrogenated ramnate to produce anaviation grade fuel.

JAMES A. ANDERSON, JR.

